1. Field of the Invention
The present invention relates to a light guiding member, an illumination apparatus, and a projector.
2. Description of the Related Art
In conventional condensing illumination apparatuses which efficiently illuminate specific areas, such as a car headlight, a stand light, a spotlight, a flashlight, and an illumination unit for a data projector, illumination has heretofore been performed usually with a high condensing performance by a comparatively simple method. In the method, a light emitting source is relatively close to a point light source, light is reflected by a reflection unit whose reflection shape is specially designed, and directivity of beams of the reflected light is enhanced by an optical lens or the like.
There has been a strong demand for enhancement of the condensing performance to obtain brighter illuminative light without excessively enlarging a size of the apparatus itself in the same manner as in general illumination. However, in general, the size tends to increase in order to obtain a brighter illuminative light, but an applied power of the light emitting source needs to be increased to enhance an output. Alternatively, a relatively enlarged reflection unit or an optical lens is applied with respect to the light emitting source in order to improve the condensing performance.
Therefore, to obtain brightness with a good condensing efficiency, the size of an illumination apparatus has to necessarily increase with respect to the light emitting source. In other words, when there is a small-sized light emitting source having a high output, similar to a point light source, the whole illumination apparatus can be miniaturized. From this demand, the miniaturization of the light emitting source is advanced even in a conventional system. Especially, an example of an effective means is a small-sized light emitting source of an electric discharge type, in which a high output is possible. Additionally, even the small-sized electric discharge type light emitting source is required to be driven by a high-voltage power supply, which makes it difficult to reduce a circuit scale. Thus, the illumination apparatus overall has many problems as regards miniaturization, and it is said that the apparatus has almost come close to its limitation.
On the other hand, nowadays, a light emitting diode (hereinafter referred to as an LED) has received much attention as the next-generation small-sized light emitting source. The LED has heretofore had advantages such as a small size, high resistance properties, and long life, but has been applied mainly as indicator illumination for various measuring instruments or a confirmation lamp of a control state due to restrictions of light emitting efficiency and output. However, in recent years, the light emitting efficiency has been rapidly improved, and it is said to be a matter of time before the light emitting efficiency exceeds that of an electric discharge type high-pressure mercury lamp or a fluorescent lamp which has heretofore had the highest efficiency. Due to the development of the high-efficiency high-luminance LED, applications therefore have rapidly increased. In recent years, a blue LED has been brought into a practical use stage in addition to conventional red and green LEDs, and this accelerates the number of applications. In fact, by the use of a plurality of high-efficiency high-luminance LEDs, actual utilization for traffic signals, outdoor large-sized full color displays, various lamps for automobiles, and a backlight for liquid crystal displays of cellular phones has been realized, whereas this has heretofore been impossible in respect of the brightness or efficiency.
There is also an example in which, due to the superior qualities of the LED, the LED is applied as the illumination apparatus for a projector display apparatus. A plurality of LEDs are constituted, accordingly a quantity of light is secured, some light beams are condensed from individual light emitting sources by an optical device such as an optical lens, and the light beams are controlled in such a manner that an irradiating light modulation device provides an allowable incident angle. As devices for converting the light in such a manner as to reduce the NA, and obtaining light having so-called high parallelism, there are Jpn. Pat. No. 3048353, Jpn. Pat. Appln. KOKAI Publication No. 2000-231344 and the like. In the light modulation device like a generally used liquid crystal device, since the allowable incident angle of the illuminative light is very small, it is supposed as ideal to form irradiation light beams having not only good condensing performance but also higher parallelism. This is a very important point for enhancing light use efficiency in the light modulation device.